Mice start looking for a nice winter home about the same time you're putting the RV up for the winter. Your RV is a perfect place for them, dry, wind proof, off the ground, deserted, and possibly even heated. These furry little creatures are highly destructive too, they will chew cloth such as curtains or furniture, wiring and electronic equipment.
Mice are relatively small to begin with, and they only need a tiny opening to get into the RV. The underside of an RV has a few holes that will allow them through. The only way to find them, is to get underneath of it, and look for them. You'll have to really scrutinize the underside of the rig. If you find any opening underneath the rig that you can fit your baby finger into, then you need to close that opening. Some people recommend stuffing it with aluminum or brass wool, it won't rust like steel wool does. Having a can of spray of expanding insulation works well too, though it can be messy if you get it on you. Hope this helps in making plans to winterize your RV.
